Photoelectric cell circuit



Dec, 23, 1941. ALBERSHEIM 2,267,690

PHOTOELECTRIC CELL CIRCUIT Filed Dec. 21, 1937 nvvs/vron 5 WJALBERSHE/M @l-Ulqdt ATTORNEY Patented Dec. 23, 1941 PHOTOELECTRIC CELL CIRCUIT Walter J. Albersheim, Great Neck, N. Y., assignor to Electrical Research Products, Inc., New York, N. Y., a corporation of Delaware Application December 21, 1937, Serial No. 180,950

In Great Britain January 11, 1937 7 Claims. (01. 179-1003) I This invention relates to photoelectric cell and amplifier circuits, and especially to apparatus employing such circuits for producing electric currents varying in accordance with sound recorded photographically upon a film.

When the sound is recorded in the form of two complementary records in opposed phase relation in a single track to form a push-pull sound record, two photoelectric cells, or photoelectric cell elements, must be employed, one for each complementary record. When the sound is recorded in the form of a single sound record, a single photoelectric cell may be employed, or two photoelectric cell elements in parallel.

The object of the present invention is an apparatus which will efficiently reproduce a pushpull film sound record and may be easily switched to efliciently reproduce a single sound record.

A feature of the invention is a resistance-capacitance coupling network for two independent photoelectric cells, or a double photoelectric cell in which either the anodes or the cathodes of the double cell are internally connected, which will accurately reproduce two complementary records so as to produce a true push-pull effect.

Another feature of the invention is a switching arrangement to change the network from pushpull operation to parallel operation Without material change in the gain or frequency charac teristic of the network.

A further feature of the invention is a network for coupling a high impedance device, such as a photoelectric cell, to another device, such as the input of a thermionic amplifier, through a transmission line of high capacitance, such as a shielded cable without material loss of the higher frequencies.

A further feature of the invention is a thermionic amplifier in which a portion of the output of the amplifier is fed back negatively in parallel relationship with the transmission line to reduce the apparent impedance of the input circuit of the amplifier attached to the line.

In the drawing:

Fig. 1 diagrammatically shows a photoelectric cell network and amplifier circuit accordingto the invention; and

Fig. 2 diagrammatically shows an alternative arrangement of the circuit.

In Fig. 1, the photoelectric cell I may have a double cathode II, I2 and two anodes I3, I4 contained within a single envelope, or, as shown in Fig. 2, two separate cells may be used. The anode I3 is connected through resistor I5 to the positive pole of a source of polarizing potential II, the

anode I4 being similarly connected through the resistor I6 to the same source H. The negative pole of the source I1 is connected through resistor I8 to the cathodes I I, I2. The resistors I5, I6 form with the photoelectric cell elements a bridge circuit.

The anode I3 is connected to a switch contact I9, and the anode I4 is connected to the other contact 20 of the switch. In reproducing a standard single record, the contacts I9, 20 are closed, connecting the anodes I3 and I4 together and the capacitor 2i across the resistors I5, I6. The switch contacts 22, 23 are also closed connecting the resistor 21 from the grounded side of the transmission line, through the switch contacts 22, 23 to the ungrounded side of the transmission line, thus reducing the apparent impedance of the photoelectric cells and network, as viewed from the transmission line, and. making the transmission efiiciency substantially the same as in the push-pull position. i

The pulsations in the currents of the photoelectric cells I I, I3 and I2, I 4 due to the variations in the light from the record are in phase, and

' produce like variations of potential across the resistors I5, I6 which are transmitted through capacitor 2| and source I1 to appear as a pulsating difference of potential across the resistor I8. The differences of potential developed across the resistor I8 are transmitted through resistor 28 to the terminals of resistor 21 which is in parallel relationship with the transmission line.

To convert the network for the reproduction of push-pull records, the contacts I9, 20 and 22, 23 are opened and the contacts 25, 26 closed, connecting the capacitor 24 from the anode I3 to the ungrounded side of the transmission line. The anode I3 is thus connected through capacitor 24 .and resistor 28 to cathode I I, and anode I4 is connected through capacitor 2| and resistor I8 to cathode I2. If the light impressed upon the photoelectric cell II, I3 increases, a current will flow from cathode II through resistor 28 and capacitor 24 to anode I3. If, at the same time, the light impressed upon the photoelectric cell I2, I4 decreases a similar amount, the current in the resistor I8 will decrease, which is equivalent to a current flowing from the anode I4 through capacitor 2| and resistor I8 to cathode I2. The voltage drops produced in the resistors I8 and 28 are thus in the proper direction to add together and produce a combined voltage across the transmission line. The voltages produced in the photoelectric cells, which, like the push-pull sound records, are opposed in phase are thus combined to produce voltages across the transmission line which are in phase and a true push-pull action is produced.

The voltages developed across the resistor 21, or those developed across the resistors l8 and 28 are supplied through the transmission line 29, which may have the form of a shielded cable as shown, to the resistor 30 in the input of the amplifying device 3 I. The amplifying device 3| may be of any desired type, such as the suppressor grid pentode diagrammatically illustrated. The output of the device 31 is supplied through the output transformer 32, to any utilization circuit, such as a sound reproducer or rerecording device, further amplification being used if desired.

The source 33 supplies current through the transformer 32 to the anode of the, device .31 and to the screen grid. The resistor 30 may be a conventional grid biasing resistor.

The resistor 35 and capacitor 30, in parallel relationship with the primary winding of the transformer 32 form a'frequency discriminative voltage divider. A portion of the output voltage of the'device 3! is thus fed back through the capacitor 31 and resistor 38 to the input circuit of the device 3!, effectively in parallel relationship with the resistor 30. The effect of this feedback is to reduce the apparent impedance of the input circuit of the device 31 as viewed from the transmission line and thus reduce the loss at high frequencies. As the voltage fed back from the drop across the capacitor 30 decreases with increasing frequency the device 3| may be given a gain frequency characteristic which rises at the higher frequencies to further compensate for any losses. Thus, the complete circuit may have a gain-frequency characteristic which is substantially fiat, or which rises atthe higher frequencies as desired.

.The coupling network in Fig. 2 is similar to the network in Fig. 1, and elements having similar functionsv in the figures have been similarly designated. In Fig. 2 separate photoelectric cells have been shown in place of the combined photoelectric cellv shown inFig. 1 and a simpler form of key is shown. It will be obvious that either type of cell or key may be used in either figure. Theoperation of the network in Fig. 2 is similar to the operation of the network in Fig. 1 as described hereinabove. I ,The source of power may be a battery or a rectifier energized by an alternating current power supply. The series impedances i1, i2 and shunt capacitors 33, Ml filter out, any noise or pulsations from the source of power. The bleeder resistor 15 stabilizes the voltage delivered from the source of power. Due to the capacitor 24, the resistor 35 has little effect upon the action of the photoelectric cell network, which is the same asdescribed hereinabove in connection with Fig. 1.

The output from the network is applied through the transmission lineand the series capacitor dividing network for the screen grid of the device .31.

The resistor 52 reduces the voltage supplied to the anode of device 3! and, with its associated capacitor, decouples the anode circuit and reduces undesired coupling effects.

The output of the device 3| is supplied through an output transformer 32, or other coupling device, to a transmission line, which may include an unbalanced attenuator 53, 54. The changes in the impedance of the attenuator 53, 54 will be reflected through the transformer 32 and will cause the voltage drop across the primary of the transformer 32 to change with changes in the setting of the attenuator. If the feedback voltage were derived from the voltage drop across the primary winding of the transformer 32, this effect would cause the feedback voltage to change materially with the changes in the attenuator 53, 54 or other similar device in the transmission line. The feedback voltage is therefore derived from the voltage drop in a resistor 55 intercalated in the anode circuit, and is supplied through resistor 38 and capacitor 31 to the input circuit of the device 31. The change in feedback voltage with change in the impedance of the output circuit is thus materially reduced.

Ina practical embodiment of the invention as shown in Fig. 2 the various elements had the following values: A Western Electric 9A photoelectric cell was used with a Western Electric 479G key, resistors l5, l0 and 21 were 4 megohms, resistors 18 and 28 were 2 megohms, capacitors 2i and 2 were 0.01 microfarad, capacitor 00 was 0.02.microfarad, resistor 01 was 3 megohms, resistors 40 and 49 were 100,000 ohms, resistor 34 was 1,000 ohms, the amplifier St was a Western Electric 310A vacuum tube, resistors ti and 12 were 50,000 ohms, resistor was 100,000 ohms, capacitors 423, M. were 8 microfarads, resistor 50 was 40,000 ohms, resistor 5| was 75,000 ohms, the source 00 was about 200 volts, resistor 52 was 45,000 ohms, resistor was 20,000 ohms, resistor 30 was 1.5 megohms, capacitor 3?, .001 or .02 microfarad, transformer 32 similar tothe Western Electric 132C output transformer, attenuator 53 was a Daven FP-39 attenuator, and 54 was a Western Electric TA-4190potentiometer,

while the undesignated by-pass capacitors were about 0.5 microfarad. While specific details are given of one practical embodiment of the invention, the invention is not in any way limited to the values cited, but many other combinations of elements may be used and still be within the scope of the claims.

What is claimed is:

1. In a film sound reproducing system, a pair of resistors and a pair of photoelectric cell elements connected to form a bridge circuit, one set of similar electrodes of said cells being joined .to a terminal of said bridge, a second pair of resistors connected in serial relationship, the junction of said resistors being connected to said set of similar electrodes, a source of polarizing potential connected from the free end of one of said second pair of resistors to the junction of said first pair of resistors, a capacitor connected from the said free end of said resistor to the junction of one of said first resistors and one pair of said elements, switching means for connecting the said junction of said first resistor and said element to the similar junction of the other of said first resistors and the other element or, at

and as opposite arms a pair of resistors in serial relationship, a second pair of resistors in serial relationship, the junction of said resistors being connected to the junction of said elements, a source of polarizing potential connected from the junction of said first pair of resistors to the free end of one of said second pair of resistors, a pair of capacitorsconnected respectively from the ends of a conjugate arm of said bridge to the free ends of said second pair of resistors and a transmission line connected to the free ends of said second pair of resistors, whereby excitations of said photoelectric elements in opposed phase produces voltages across said transmission line in the same phase.

3. Light sensitive apparatus comprising a pair of photoelectric elements in parallel relationship, a pair of resistors in parallel relationship connected in serial relationship with said elements, a second pair of resistors in serial relationship, the junction of said resistors being connected to similar electrodes of said elements, a capacitor connected from the other electrodes of said elements to the free end of one of said second pair of resistors, a source of polarizing potential connected from said free end to said first pair of resistors, a transmission line of relatively high capacitance connected to the free ends of second pair of resistors, a thermionic amplifying device connected to said line, means for feeding back a portion of the output of said device in reversed phase to said transmission line whereby the input impedance of said device is eiiectively decreased,

4. In combination, a source of signal currents having inherently a relatively high impedance, a transmission line having a relatively large shunt capacitance, a network for connecting said source to one end of said line, a thermionic amplifier having an input and an output circuit, means for connecting said line to the input circult of said amplifier, and means for feeding back energy from the output circuit of said amplifier in shunt to the input circuit and transmission line, in such phase as to reduce the apparent impedance of the input circuit whereby the relative loss of high frequencies in said transmission line is materially reduced.

5. In a. film sound reproducing system a bridge circuit having as adjacent arms the current paths of a pair of light sensitive elements and as opposite arms a pair of resistors in serial relationship, a second pair of resistors in serial relationship, the junction of said second pair of resistors being connected to the junction of said elements, a source of polarizing potential connected from the junction of said first pair of resistors to the free end of one of said second pair of resistors, a capacitor connected from one end of the conjugate arm of said bridge to said free end of said resistor, a transmission line connected to the free ends of said second pair of resistors, an amplifier connected to the other end of said line, switching means for connecting a second capacitor from the other end of said conjugate arm to the free end of the other of said second resistors, and, at will, breaking said connection and connecting both ends of said conjugate arm, and connecting a resistor across said transmission line, whereby the output of said network for equal illumination is substantially equal for both positions of said switching means.

6. A system for photcelectrically scanning balanced two track sound records, including in a circuit two light sensitive elements, one for each of said two sound tracks, means for connecting said two light sensitive elements as to direct current parallel to each other, with like polarities connected with each other, while connecting said light sensitive elements as to alternating current in opposition to each other and in series, said means including two serially arranged resistances, one ior each said two light sensitive elements and arranged to combine the output of the same, a single amplifier tube, and means for directly connecting the outer ends of said two serially arranged resistances with said amplifier tube.

7. A system for photcelectrically scanning balanced two track sound records, including in a circuit two light sensitive means, one for each of said two sound tracks, means for connecting said two light sensitive means as to direct current parallel to each other, with like polarities connected with each other, while also connecting said light sensitive means as to alternating current in opposition to each other and in series, said means including two serially arranged resistances, one for each said two light sensitive means and arranged to combine the output of the same, a single amplifier tube, and means for directly connecting the outer ends of said two serially arranged resistances with said amplifier tube, said light sensitive means consisting of a photoelectric tube including within a vessel two separate anodes and a single cathode common to both said anodes.

WALTER J. ALBERSHEIM. 

